1. Field of the Invention
The present invention relates to a magnetic disc device which employs a flexible magnetic disc as a recording medium, and more particularly, to a magnetic disc device for double-sided media.
2. Description of the Prior Art
Heretofore, for magnetic disc devices of this kind use has been made widely of a system in which one magnetic head unit is held fixed, and the other magnetic head unit is movably supported in a direction perpendicular to the plane of the magnetic disc and in two directions of rotation, namely, the rotational direction and the radial direction of the magnetic disc (see, U.S. Pat. No. 4,151,573).
This structure makes the positioning of the magnetic head easy. However, the magnetic disc bends to follow the shape of the magnetic head so that if the rigidity of the magnetic disc is high, the disc appears wavy and the magnetic head tends to stay away from portions of the magnetic disc, without being able to make contact with the entire disc. Therefore, such a system can be used only where the rigidity of the magnetic disc is sufficiently low. Further, the fact that the magnetic disc has to be bent to follow the magnetic head gives rise to a drawback in that the durability of the magnetic disc is reduced.
Moreover, this system has another disadvantage, for instance, in that the positional relationship between the magnetic disc and the fixed magnetic head has to be controlled with high accuracy.
A device has been proposed in which both of the magnetic heads are movably supported in three directions of up-down, rolling, and pitching (see, U.S. Pat. No. 4,306,258). In such a structure, flexibility in three directions is provided by a sheet of gimbal plate, but the gimbal plate cannot be made too hard or it may break due to plastic deformation. Moreover, if the elasticity in the two directions of rotation is too large, the two magnetic heads must be accurately maintained parallel to one another, otherwise, the pressing load forcing the two magnetic heads against the magnetic disc, which are tilted due to mounting errors, must be increased in order to maintain a close contact between the heads and the disc. As a result, this can lead to a reduction in productivity and deterioration in the durability of the magnetic disc.
Magnetic discs with increased memory capacity and smaller diameter have been used more widely in recent years. A reduction in the magnetic disc diameter results in an increase in its rigidity. This leads to difficulties in bringing the magnetic disc into continuous contact with the magnetic head, if the method of supporting the magnetic head described above is employed. Therefore, it is necessary to improve the planar accuracy of the magnetic disc, improve the vertical accuracy in attaching the magnetic head, or increase the pressing load on the head. Because of this, problems, such as a degradation of durability of the magnetic disc and degradation of productivity, have arisen. These problems become more pronounced when the rotational rigidity of the magnetic disc is greater than necessary.
As discussed above, the requirement for reducing the elasticity of the magnetic disc in the direction perpendicular to the plane of the magnetic disc has not been met sufficiently in the prior-art supporting method.
In addition, applicant has found that it is necessary to optimize the elasticity in the respective directions of rolling and pitching of the gimbal plate. More specifically, it has been found that it is desirable to increase the elasticity in the rolling direction. Also, when the recording density of the magnetic disc is increased, it desirable to increase the elasticity in the pitching direction in order to decrease the deviation of the head in the azimuthal direction. However, existing magnetic disc devices have similar structures in the rolling direction and in the pitching direction of the gimbal plate, so that the elasticities in the rolling and pitching directions are approximately equal. Consequently, due to the fact that the gimbal plate in the existing magnetic disc devices must be dictated by the larger of the elasticities in the rolling and pitching directions, it is difficult to precisely control the elasticity both in the rolling direction and in the pitching direction.